Method and apparatus for handover and reestablishment in a wireless communication system
Embodiments of the present disclosure relate to methods and apparatuses for handover and reestablishment in a wireless communication system. According to some embodiments of the disclosure, a method may include: receiving, at a user equipment (UE), a radio resource control (RRC) reconfiguration message including a path switch indication and a list of candidate relays; selecting a target relay from the list of candidate relays; and establishing a PC5 RRC connection with the target relay. Furthermore, the UE may select another target relay for path switch if a path switch failure associated with the first selected target relay happens.
1 . A user equipment (UE) for wireless communication, comprising:
at least one memory;
at least one processor coupled with the at least one memory and configured to:
receive a radio resource control (RRC) reconfiguration message including a path switch indication and a list of candidate relays,
wherein the list of candidate relays includes one or more candidate relays, and
wherein the RRC reconfiguration message includes:
an indication of whether a consecutive path switch is allowed or not,
a maximum number of consecutive path switches, or
a value of a timer for the consecutive path switch;
select a target relay from the list of candidate relays; and
transmit an RRC reconfiguration sidelink message to the target relay.
2 . The UE of claim 1 , wherein the UE selects the target relay from the list of candidate relays by:
selecting the first candidate relay in the list of candidate relays as the target relay;
selecting a candidate relay from the list of candidate relays in response to the channel quality between the candidate relay and the UE being equal to or greater than a threshold; or
selecting a candidate relay from the list of candidate relays in response to a PC5 connection being established between the UE and the candidate relay.
3 . The UE of claim 1 , wherein the at least one processor is further configured to cause the UE to:
set a counter for consecutive path switch to an initial value in response to receiving the RRC reconfiguration message when the maximum number of consecutive path switches is indicated in the RRC reconfiguration message; or
start the timer for the consecutive path switch in response to receiving the RRC reconfiguration message when the value of the timer for the consecutive path switch is indicated in the RRC reconfiguration message.
4 . The UE of claim 3 , wherein the at least one processor is further configured to, in response to a failure to connect to the target relay, cause the UE to:
select a second target relay from the list of candidate relays;
transmit a second RRC reconfiguration sidelink message to the second target relay; and
increment the counter for the consecutive path switch by a value.
5 . The UE of claim 4 , wherein the at least one processor is further configured to, in response to receiving an RRC reconfiguration complete sidelink message from the second target relay, cause the UE to:
stop the timer for the consecutive path switch or reset the counter for the consecutive path switch; and
transmit an RRC reconfiguration complete message, wherein the RRC reconfiguration complete message indicates an ID of the target relay.
6 . The UE of claim 4 , wherein the at least one processor is further configured to cause the UE to:
in response to the value of the counter for the consecutive path switch being equal to or greater than the maximum number of the consecutive path switch or the expiry of the timer for the consecutive path switch, initiate a reestablishment procedure.
7 . The UE of claim 1 , wherein the at least one processor is further configured to cause the UE to:
start a mobility timer in response to receiving the RRC reconfiguration message;
start a sidelink reconfiguration timer in response to transmitting the RRC reconfiguration sidelink message; and
stop the mobility timer and the sidelink reconfiguration timer in response to receiving an RRC reconfiguration complete sidelink message.
8 . A processor for wireless communication, the processor comprising:
at least one memory;
a controller coupled with the at least one memory and configured to cause the processor to:
receive a radio resource control (RRC) reconfiguration message including a path switch indication and a list of candidate relays,
wherein the list of candidate relays includes one or more candidate relays, and
wherein the RRC reconfiguration message includes:
an indication of whether a consecutive path switch is allowed or not,
a maximum number of consecutive path switches, or
a value of a timer for the consecutive path switch;
select a target relay from the list of candidate relays; and
transmit an RRC reconfiguration sidelink message to the target relay.
9 . The processor of claim 8 , wherein the processor selects the target relay from the list of candidate relays by:
selecting the first candidate relay in the list of candidate relays as the target relay;
selecting a candidate relay from the list of candidate relays in response to the channel quality between the candidate relay and the processor being equal to or greater than a threshold; or
selecting a candidate relay from the list of candidate relays in response to a PC5 connection being established between the processor and the candidate relay.
10 . A method performed by a user equipment (UE), the method comprising:
receiving a radio resource control (RRC) reconfiguration message including a path switch indication and a list of candidate relays,
wherein the list of candidate relays includes one or more candidate relays, and
wherein the RRC reconfiguration message includes:
an indication of whether a consecutive path switch is allowed or not,
a maximum number of consecutive path switches, or
a value of a timer for the consecutive path switch;
selecting a target relay from the list of candidate relays; and
transmitting an RRC reconfiguration sidelink message to the target relay.
11 . The method of claim 10 , wherein selecting the target relay from the list of candidate relays includes:
selecting the first candidate relay in the list of candidate relays as the target relay;
selecting a candidate relay from the list of candidate relays in response to the channel quality between the candidate relay and the UE being equal to or greater than a threshold; or
selecting a candidate relay from the list of candidate relays in response to a PC5 connection being established between the UE and the candidate relay.
12 . The method of claim 10 , further comprising:
setting a counter for consecutive path switch to an initial value in response to receiving the RRC reconfiguration message when the maximum number of consecutive path switches is indicated in the RRC reconfiguration message; or
starting the timer for the consecutive path switch in response to receiving the RRC reconfiguration message when the value of the timer for the consecutive path switch is indicated in the RRC reconfiguration message.
13 . The method of claim 12 , further comprising:
selecting a second target relay from the list of candidate relays;
transmitting a second RRC reconfiguration sidelink message to the second target relay; and
incrementing the counter for the consecutive path switch by a value.
14 . The method of claim 13 , further comprising:
in response to receiving an RRC reconfiguration complete sidelink message from the second target relay, stopping the timer for the consecutive path switch or resetting the counter for the consecutive path switch; and
transmitting an RRC reconfiguration complete message, wherein the RRC reconfiguration complete message indicates an ID of the target relay.
15 . The method of claim 13 , further comprising:
in response to the value of the counter for the consecutive path switch being equal to or greater than the maximum number of the consecutive path switch or the expiry of the timer for the consecutive path switch, initiating a reestablishment procedure.
16 . The method of claim 10 , further comprising:
starting a mobility timer in response to receiving the RRC reconfiguration message;
starting a sidelink reconfiguration timer in response to transmitting the RRC reconfiguration sidelink message; and
stopping the mobility timer and the sidelink reconfiguration timer in response to receiving an RRC reconfiguration complete sidelink message.
17 . A user equipment (UE) for wireless communication, comprising:
at least one memory;
at least one processor coupled with the at least one memory and configured to:
receive a radio resource control (RRC) reconfiguration message including a path switch indication and a list of candidate relays,
wherein the list of candidate relays includes one or more candidate relays;
select a target relay from the list of candidate relays;
transmit an RRC reconfiguration sidelink message to the target relay;
start a mobility timer in response to receiving the RRC reconfiguration message;
start a sidelink reconfiguration timer in response to transmitting the RRC reconfiguration sidelink message; and
stop the mobility timer and the sidelink reconfiguration timer in response to receiving an RRC reconfiguration complete sidelink message.